The present invention concerns apparatus for the electrochemical detection of the oxygen content of liquids by measurement of an electric current between two electrodes made from different materials immersed in the liquid, which electrodes are, with the exception of their effective free end surfaces, fully embedded in insulating material, wherein for cleaning the free electrode end surfaces a grinding device is pressed by means of at least one spring both to the free electrode end surfaces and to the adjacent surface area portions of the insulating material and the electrodes are so shaped and arranged that in the course of continued grinding of the electrodes and the insulating material, the shape, size and mutual spacing of the effective end surfaces remain unchanged.
An apparatus of the above type is disclosed in Swiss Pat. No. 469,981. According to this patent the two electrodes are formed by coaxially arranged pipe sections which are radially spaced apart, the pipe sections being fully embedded in an electrically insulating synthetic material body with the exception of one of their end surfaces lying on the same axial slide. To clean the effective, free electrode end surfaces a grinding organ is provided which is rotatable by a driving device around the axis of the tube sections, the grinding body having a grinding surface bearing against the free end surfaces of the pipe sections and the surface portions of the synthetic resin body adjacent to these end surfaces, and is pressed against the noted surfaces under the bias of a spring. Although this known apparatus has proved itself well in practice, it has a disadvantage which in certain circumstances is troublesome, i.e. because of the different hardness, abrasion-resistance and corrosion properties of the two electrodes consisting of different materials, a fully uniform wear or abrasion by means of the common grinding body is not always assured and various deposits of grinding particles may adhere to the free ends of the electrode end surfaces. This may result in variations in the electrochemical properties of the free electrode end surfaces, whereby the accuracy of the oxygen measurements is impaired or a frequent recalibration of the measurement apparatus becomes necessary.